The present invention relates to subterranean cementing operations and, more particularly, to cement compositions comprising improved lost circulation materials, and methods of using such cement compositions in subterranean formations.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
Subterranean formations traversed by well bores often may be weak, highly permeable, and extensively fractured. In some cases, such formations may be unable to withstand the hydrostatic pressure normally associated with fluids (e.g., cement compositions and the like) being injected into the formation. In such cases, the hydrostatic pressure may be sufficient to force such fluids into the natural or created fractures and/or permeable zones of the formation, which may result in a significant loss of fluid into the formation. This loss of fluid circulation may be problematic for a number of reasons. For example, where the loss of circulation occurs during a cementing operation, excessive fluid loss may cause a cement composition to dehydrate prematurely. Premature dehydration of the cement composition may excessively viscosify the cement composition, and potentially may cause an operator to terminate the cementing operation, wash out the cement composition from the well bore, and restart the cementing operation anew.
Previous attempts to minimize the loss of circulation into the subterranean formation have involved adding a variety of additives, including, but not limited to, asphaltenes, ground coal, cellulosic materials, plastic materials, walnut hulls, sized waste formica, and the like, to the cement composition. Such additives have been included, for example, to attempt to plug or bridge formation fractures and/or the permeable zones in the formation where the treatment fluids typically may be lost. However, conventional materials often are not rigid, and thus a greater concentration of these materials may be required to effectively prevent the loss of circulation during a cementing operation.
Polyethylene is used extensively in manufacturing, for instance, trash cans, buckets, baskets, and other materials of commerce. With time, the plasticizer that often is a component of a typical polyethylene product may begin to degrade, which may cause the polyethylene to become increasingly brittle, which may reduce its usable life. Consumers generally have no use for brittle polyethylene materials and often discard or otherwise dispose of them, commonly in a landfill, where the polyethylene may reside indefinitely, because it generally does not deteriorate until after a very long time.